Ink composition, process for producing the same, method of forming image therewith and image forming device

ABSTRACT

An ink composition contains particles having a solid coloring material substantially enclosed by a block polymer, and a solvent. The solid coloring material is enclosed in a micelle formed of the block polymer, and preferably 90 wt % or more of the solid coloring material are enclosed by the block polymer. The average particle size of the particles is 200 nm or less. A method for producing an ink composition includes forming the particles by insolubilizing the coloring material and the block polymer in a state of both being dissolved in a solution. The above described ink composition has an adequate dispersibility of the coloring material and is suitable for an ink composition for an ink-jet device.

TECHNICAL FIELD

The present invention relates to an ink composition containing a polymerwhich can be used as a variety of functional materials, a productionmethod therefor, and an image-forming method and an image-forming deviceusing it. The present invention particularly relates to the inkcomposition comprising an aqueous dispersive material useful for animage-forming material preferably usable for a printer, a display andthe like, and the image-forming method and the image-forming deviceusing the ink composition.

BACKGROUND ART

An aqueous dispersive material containing a granular solid has beenconventionally and widely used for agricultural chemicals such as aherbicide and an insecticide, and medicines such as an anticancer drug,an antiallergic agent and an anti-inflammatory agent, as a functionalmaterial. In addition, a coloring material such as ink and toner, whichcontains a coloring agent of a granular solid, is well known. In recentyears, a digital printing technology has been progressing by leaps andbounds. The digital printing technology, which is represented by anelectrophotographic technology and an ink-jet technology, has beenincreasing its presence as an imaging technology in offices and homes inrecent years.

Among them, an ink-jet technology is a direct recording method, and hasstriking characteristics of compactness and low power consumption. Inaddition, the picture quality has been rapidly improved owing to arefined nozzle. One example of the ink-jet technologies is a process ofevaporating and foaming an ink supplied from an ink tank by heating itwith a heater in a nozzle, and discharging the ink to form an image on arecording medium. Another example is a method of discharging the inkfrom the nozzle by vibrating a piezoelectric element.

Because the ink used for these methods is usually an aqueous dyesolution, it might have caused blurring or a phenomenon calledfeathering along a fiber direction of paper at recorded portions on arecording medium, when colors have been superposed. It has beeninvestigated to use a pigment-dispersed ink for the purpose of improvingthe phenomena. For instance, a method is proposed which dispersespigment with an ionic block polymer having each one or more componentsof a hydrophilic component and a hydrophobic component (U.S. Pat. No.5,085,698). However, such improvements are still desired to the methodas inhibiting coagulation between particles due to mutual interaction,dispersing them in a solvent for a long time, tint, coloring andfixability.

DISCLOSURE OF THE INVENTION

The present invention is designed with respect to such problems inconventional methods, and is directed at providing an ink compositionhaving an adequate dispersibility of a coloring material, and providinga production method therefor.

In addition, the present invention directs at providing the inkcomposition for an ink-jet device, which has adequate fixability andfurther adequate tint and coloring of a printed image, and providing aproduction method therefor.

In addition, the present invention directs at providing an image-formingmethod with the use of the above described ink composition, and animage-forming device used for it.

Specifically, the first of the present invention is an ink compositioncharacterized in that the particles of a solid coloring material areenclosed in a micelle formed of block polymer.

The above described ink composition is preferably a dispersion inkcomposition.

The above described solid coloring material in an amount of preferably90 wt % or more, more preferably 98 wt % or more, and further preferably98 wt % or more with respect to the total solid coloring material isenclosed by the block polymer.

The average particle size of the above described particles is preferably200 nm or smaller.

In addition, an ink composition according to the present invention ispreferably an ink composition for an ink-jet device.

The second of the present invention is a method for producing an inkcomposition, characterized by a step of forming particles byinsolubilizing a coloring material and a block polymer in a state ofboth being dissolved in a solution.

In addition, another aspect of the present invention is a method forproducing an ink composition, characterized by a step of formingparticles by adding and dispersing a coloring material dissolved in asolution into a solvent dispersion having block polymer forming amicelle.

The third invention is an image-forming method for recording an image bygiving an ink onto a medium to be recorded, characterized in that theink is the above described ink composition.

The fourth invention is an image-forming device used for the abovedescribed image-forming method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a schematic mechanism of an image-recordingdevice according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Below, the present invention will be described in detail.

The first of the present invention is a dispersion ink compositioncharacterized in that the dispersion ink contains the particles of asolid coloring material substantially enclosed by block polymer, and asolvent. In the present invention, the solid coloring material is usedin a characteristic manner.

Here, enclosure refers to a state of being wrapped inside block polymer.It refers to, for instance, the state in which a coloring materialexists in a hydrophobic core of a micelle formed of block polymer inwater.

The solid coloring material refers to a coloring material in a crystalstate or a vitrified state, which, for instance, includes a solidifiedmaterial of a pigment or a dye, a crystallized material and a vitrifiedcoloring material. The examples are shown below.

A pigment mainly refers to a coloring agent of a powdery particulate,which is insoluble in water and an organic solvent, and may be any of anorganic pigment and an inorganic pigment. As a pigment used for ink, ablack pigment and primary color pigments of cyan, magenta, yellow, red,green and blue can be preferably used. In addition, a color pigmentother than the above described pigments, an achromatic or light-coloredpigment, or a pigment with a metallic luster may be used. In addition,new synthetic pigment may be used for the present invention.

Furthermore, the pigment to be used has desirably the average primaryparticle size of 50 nm, can employ commercially available pigment, andcan employ a pigment which has been refined (mechanically crushed bymilling, for instance) and classified, as well.

Below, commercially available pigments of black, cyan, magenta andyellow are exemplified.

Examples of black pigments include, but not limited to, Raven 1060,Raven 1080, Raven 1170, Raven 1200, Raven 1250, Raven 1255, Raven 1500,Raven 2000, Raven 3500, Raven 5250, Raven 5750, Raven 7000, Raven 5000ULTRA II, Raven 1190 ULTRA II (all of the above, from Columbian CarbonCompany), Black Pearls L, MOGUL-L, Regal 400R, Regal 660R, Regal 330R,Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1300,Monarch 1400 (all of the above, from Cabot Corporation), Color BlackFW1, Color Black FW2, Color Black FW200, Color Black 18, Color BlackS160, Color Black S170, Special Black 4, Special Black 4A, Special Black6, Printex 35, Printex U, Printex 140U, Printex V, Printex 140V (all ofthe above, from Degussa AG), No. 25, No. 33, No. 40, No. 47, No. 52, No.900, No. 2300, MCF-88, MA600, MA7, MA8, and MA100 (all of the above,from Mitsubishi Chemical Corporation).

Examples of cyan pigments include, but not limited to, C. I. PigmentBlue-1, C. I. Pigment Blue-2, C. I. Pigment Blue-3, C. I. PigmentBlue-15, C. I. Pigment Blue-15:2, C. I. Pigment Blue-15:3, C. I. PigmentBlue-15:4, C. I. Pigment Blue-16, C. I. Pigment Blue-22, and C. I.Pigment Blue-60.

Examples of magenta pigments include, but not limited to, C. I. PigmentRed-5, C. I. Pigment Red-7, C. I. Pigment Red-12, C. I. Pigment Red-48,C. I. Pigment Red-48:1, C. I. Pigment Red-57, C. I. Pigment Red-112, C.I. Pigment Red-122, C. I. Pigment Red-123, C. I. Pigment Red-146, C. I.Pigment Red-168, C. I. Pigment Red-184, C. I. Pigment Red-202, and C. I.Pigment Red-207.

Examples of yellow pigments include, but not limited to, C. I. PigmentYellow-12, C. I. Pigment Yellow-13, C. I. Pigment Yellow-14, C. I.Pigment Yellow-16, C. I. Pigment Yellow-17, C. I. Pigment Yellow-74, C.I. Pigment Yellow-83, C. I. Pigment Yellow-93, C. I. Pigment Yellow-95,C. I. Pigment Yellow-97, C. I. Pigment Yellow-98, C. I. PigmentYellow-114, C. I. Pigment Yellow-128, C. I. Pigment Yellow-129, C. I.Pigment Yellow-151, and C. I. Pigment Yellow-154.

The content of the pigment used for an ink composition according to thepresent invention preferably is 0.1 to 50 wt % with respect to theweight of the ink composition. The pigment in an amount less than 0.1 wt% does not provide an adequate image density, and the pigment in anamount exceeding 50 wt % may aggravate the fixability of an image. Thefurther preferable amount of the pigment is in a range between 0.5 to 30wt %.

In addition, a dye applicable to an ink composition according to thepresent invention may be a well-known one or a new one. For instance, aswill be described below, a water-soluble dye such as a direct dye, anacid dye, a basic dye, a reactive dye and a food dye, and awater-insoluble dye such as a lipophilic (oil-soluble) dye and adisperse dye, can be used, though in a solidified state. In thisrespect, for instance, the oil-soluble dye is preferably used. Theexamples include C. I. Solvent Blue-33, -38, -42, -45, -53, -65, -67,-70, -104, -114, -115, and -135;

C. I. Solvent Red-25, -31, -86, -92, -97, -118, -132, -160, -186, -187,and -219; and

C. I. Solvent Yellow-1, -49, -62, -74, -79, -82, -83, -89, -90, -120,-121, -151, -153, and -154.

Water-soluble dyes are also usable. The examples include direct dyessuch as C. I. Direct Black-17, -19, -22, -32, -38, -51, -62, -71, -108,-146, and -154;

C. I. Direct Yellow-12, -24, -26, -44, -86, -87, -98, -100, -130, and-142;

C. I. Direct Red-1, -4, -13, -17, -23, -28, -31, -62, -79, -81, -83,-89, -227, -240, -242, and -243;

C. I. Direct Blue-6, -22, -25, -71, -78, -86, -90, -106, and -199;

C. I. Direct Orange-34, -39, -44, -46, and -60;

C. I. Direct Violet-47 and -48;

C. I. Direct Brown-109; and

C. I. Direct Green-59;

acid dyes such as C. I. Acid Black-2, -7, -24, -26, -31, -52, -63, -112,-118, -168, -172, and -208;

C. I. Acid Yellow-11, -17, -23, -25, -29, -42, -49, -61, -71;

C. I. Acid Red-1, -6, -8, -32, -37, -51, -52, -80, -85, -87, -92, -94,-115, -180, -254, -256, -289, -315, and -317;

C. I. Acid Blue-9, -22, -40, -59, -93, -102, -104, -113, -117, -120,-167, -229, -234, and -254;

C. I. Acid Orange-7 and -19;

C. I. Acid Violet-49;

reactive dyes such as C. I. Reactive Black-1, -5, -8, -13, -14, -23,-31, -34, and -39;

C. I. Reactive Yellow-2, -3, -13, -15, -17, -18, -23, -24, -37, -42,-57, -58, -64, -75,. -76, -77, -79, -81, -84, -85, -87, -88, -91, -92,-93, -95, -102, -111, -115, -116, -130, -131, -132, -133, -135, -137,-139, -140, -142, -143, -144, -145, -146, -147, -148, -151, -162, and-163;

C. I. Reactive Red-3, -13, -16, -21, -22, -23, -24, -29, -31, -33, -35,-45, -49, -55, -63, -85, -106, -109, -111, -112, -113, -114, -118, -126,-128, -130, -131, -141, -151, -170, -171, -174, -176, -177, -183, -184,-186, -187, -188, -190, -193, -194, -195, -196, -200, -201, -202, -204,-206, -218, and -221;

C. I. Reactive Blue-2, -3, -5, -8, -10, -13, -14, -15, -18, -19, -21,-25, -27, -28, -38, -39, -40, -41, -49, -52, -63, -71, -72, -74, -75,-77, -78, -79, -89, -100, -101, -104, -105, -119, -122, -147, -158,-160, -162, -166, -169, -170, -171, -172, -173, -174, -176, -179, -184,-190, -191, -194, -195, -198, -204, -211, -216, and -217;

C. I. Reactive Orange-5, -7, -11, -12, -13, -15, -16, -35, -45, -46,-56, -62, -70, -72, -74, -82, -84, -87, -91, -92, -93, -95, -97, and-99;

C. I. Reactive Violet-1, -4, -5, -6, -22, -24, -33, -36, and -38;

C. I. Reactive Green-5, -8, -12, -15, -19, and -23; and

C. I. Reactive Brown-2, -7, -8, -9, -11, -16, -17, -18, -21, -24, -26,-31, -32, and -33; and

C. I. Basic Black-2;

C. I. Basic Red-1, -2, -9, -12, -13, -14, and -27;

C. I. Basic Blue-1, -3, -5, -7, -9, -24, -25, -26, -28, and -29;

C. I. Basic Violet-7, -14, and -27; and

C. I. Food Black-1 and -2.

The examples of the above described coloring material are particularlypreferable for an ink composition according to the present invention,but the coloring material used in an ink composition according to thepresent invention is not particularly limited to the above describedcoloring material.

The content of a solidified or crystallized dye used in an inkcomposition according to the present invention is preferably 0.1 to 50wt % to the weight of the ink composition. The dye in an amount lessthan 0.1 wt % does not provide an adequate image density, and the dye inan amount exceeding 50 wt % may aggravate the fixability of an image.The further preferable amount of the dye is in a range between 0.5 to 30wt %.

In the present invention, pigment and dye may be used together.

The vitrified coloring material includes such a high polymer containinga coloring material and a high polymer complex of a coloring material ashaving a high glass transition temperature. The preferred range of thecontent for an ink composition is equivalent to that of the abovedescribed pigment and dye.

In the next place, the block polymer of the component which is furthercharacteristically used in the present invention, will be described.

The specific examples of the block polymer usable for the presentinvention include conventionally known block polymers such as acrylicand methacrylic block polymers, addition or condensation block polymersof polystyrene and another substance and block polymers having a blockof polyoxyethylene or polyoxyalkylene. In the present invention, a blockpolymer containing a polyvinyl ether structure is preferably used. Inaddition, in the present invention, the block polymer may be a graftpolymer containing a polyvinyl ether structure. The segment of the blockpolymer may be a copolymerized segment of which the form of thecopolymerization is not limited, and for instance, may be a randomsegment or a graduation segment.

A block polymer containing a polyvinyl ether structure preferably usedin the present invention will be now described. Many methods forsynthesizing a polymer containing a polyvinyl ether structure have beenreported (Japanese Patent Laid-Open No. H11-080221), but arepresentative one is a method by cation living polymerization reportedby Aoshima et al. (Japanese Patent Laid-Open No. H11-322942 and JapanesePatent Laid-Open No. H11-322866). The method for synthesizing polymersby cation living polymerization can synthesize various polymers such asa homopolymer or a copolymer consisting of two or more monomers, furthera block polymer, a graft polymer and a graduation polymer, so as toprecisely acquire equal length (molecular weight). In addition, thepolyvinyl ether can have various functional groups introduced into theside chain. The cationic polymerization can be otherwise carried out ina HI/I₂ or HCl/SnCl₄ system.

In addition, the structure of a block polymer containing a polyvinylether structure may be a copolymer comprising a vinyl ether and otherpolymers.

In the present invention, the block polymer more preferably has a blockform such as AB, ABA and ABD. A, B and D show different block segmentsfrom each other.

The block polymer with the above described polyvinyl ether structure haspreferably such a specific repeating unit structure of the polyvinylether structure as to be expressed below general formula (1):

wherein, R¹ is selected among a straight-chain, a branched or cyclicalkyl group having 1 to 18 carbon number, —(CH(R²)—CH(R³)—O)_(L)—R⁴ and—(CH₂)_(m)—(O)_(n)—R⁴; L and m are independently selected among integersof 1 to 12; n is 0 or 1; R² and R³ are independently a hydrogen atom orCH₃; R⁴ is a hydrogen atom, a straight, branched or cyclic alkyl groupof having 1 to 6 carbon numbers, Ph, Pyr, Ph-Ph, Ph-Pyr, —CHO, —CH₂CHO,—CO—CH═CH₂, —CO—C(CH₃)═CH₂ or —CH₂COOR⁵, and if R⁴ is the othersubstance than a hydrogen atom, the hydrogen atom on a carbon atom canbe replaced by a straight-chain or branched-chain alkyl group of having1 to 4 carbon numbers, F, Cl or Br, and a carbon atom in an aromaticring by a nitrogen atom, respectively; R⁵ is a hydrogen atom or an alkylgroup having 1 to 5 carbon numbers.

In the present invention, -Ph represents a phenyl group, -Pyr a pyridylgroup, -Ph-Ph a biphenyl group, and -Ph-Pyr a pyridyl phenyl group. Thepyridyl group, the pyridyl phenyl group and the biphenyl group may beany of isomers of taking a possible position.

In the present invention, an amphiphilic block polymer is preferablyemployed. For instance, the amphiphilic block polymer can be obtained byselecting a hydrophobic block segment and a hydrophilic block segmentfrom the repeating unit structure of the above described general formula(1), and synthesizing them.

In the next place, the structures of a vinyl ether monomer are writtenas the examples of the repeating unit structure for the polyvinyl etherstructure of a block polymer, but polyvinyl ether structures used in thepresent invention are not limited to these.

Wherein Me represents a methyl group, Et an ethyl group and i-Pr anisopropyl group.

The structures of a polyvinyl ether consisting of these vinyl ethermonomers are exemplified below, but a polymer used in the presentinvention is not limited to them.

In the above described polyvinyl ether, the u, v and w of a repeatingunit number are independently preferably 1 or more and 10,000 or less,and more preferably the total (u+v+w) is 10 or more and 20,000 or less.

The molecular weight distribution of the block polymer used in thepresent invention, which is equal to Mw (weight average molecularweight)/Mn (number average molecular weight), is 2.0 or less, preferably1.6 or less, further preferably 1.3 or less, and particularly preferably1.2 or less. The number average molecular weight Mn of a block polymerused in the present invention is preferably 1,000 to 300,000, furtherpreferably 5,000 or more but 100,000 or less. The number averagemolecular weight of a hydrophobic segment is preferably 5,000 or morebut 100,000 or less. The block polymer having the number averagemolecular weight Mn of less than 1000 or more than 300,000 may notadequately disperse a material which plays a predetermined function in asolvent.

In addition, in order to acquire improved dispersion stability andinclusion capability, the block polymer preferably has more flexiblemolecular mobility, because such a block polymer is easily physicallyentangled with the surface of the solid coloring material of afunctional material. In addition, as will be described in detail below,the block polymer preferably has the flexible molecular mobility also inthe respect of easily forming a coating layer on a medium to berecorded. For this purpose, the glass transition temperature Tg of amain chain of a block polymer is preferably 20° C. or lower, morepreferably 0° C. or lower and further preferably −20° C. or lower. Inthis respect as well, a polymer having a polyvinyl ether structure ispreferably used because of having a lower glass transition point andflexible characteristics.

The content of the above described block polymer in an ink compositionaccording to the present invention is 0.1 to 50 wt %, and preferably 0.5to 20 wt %. When the content of the block polymer is less than 0.1 wt %,the block polymer may not be able to adequately disperse or include thecoloring material contained in the ink composition according to thepresent invention, and when the content exceeds 50 wt %, the inkcomposition may have too high viscosity.

A solvent contained in an ink composition according to the presentinvention is not particularly limited, but means a medium capable ofdissolving, suspending, and dispersing a component contained in the ink.The solvent used in the present invention includes an organic solventsuch as various aliphatic hydrocarbons with a straight chain, a branchedchain and a cyclic chain, aromatic hydrocarbons and heteroaromatichydrocarbons; an aqueous solvent; and water. In an ink compositionaccording to the present invention, particularly water and an aqueoussolvent can be preferably used. The examples of the aqueous solventinclude polyvalent alcohols such as ethylene glycol, diethylene glycol,triethylene glycol, polyethylene glycol, propylene glycol, polypropyleneglycol and glycerin; polyalcoholic ethers such as ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monoethyl ether and diethylene glycolmonobutyl ether; and a nitrogen-containing solvent such asN-methyl-2-pyrrolidone, substituted pyrrolidone and triethanolamine. Inaddition, for an ink used for the purpose of quick drying on paper,monovalent alcohols such as methanol, ethanol and isopropyl alcohol canbe used. The usable content of a solvent, particularly of the abovedescribed water or aqueous solvent, in an ink composition according tothe present invention, is preferably in a range of 20 to 99 wt % andfurther preferably of 30 to 95 wt % with respect to the total weight ofan aqueous dispersion.

An ink composition according to the present invention is allowed tocontain other components than the above. An ink composition according tothe present invention is characterized in that a solid coloring materialis enclosed by a block polymer. When the solid coloring material isenclosed by the block polymer, the coloring material can inhibit thedecomposition of itself, and improve its coloring properties if having asmall particle size. The coloring material preferably has a specificparticle size of 200 nm or smaller by average.

The solid coloring material can be enclosed by the block polymer byadding a solution containing a coloring material dissolved in awater-insoluble organic solvent, to a micelle, for instance, formed ofblock polymer in water, and then distillation-removing the organicsolvent. The solid coloring material enclosed by the block polymer canbe formed by another method of forming the included state, throughphase-inverting a solution in a state of both a polymer and a coloringmaterial being dissolved in an organic solvent into a state of beingdispersed in a water-based solvent, and distillation-removing theremaining organic solvent. Furthermore, it can be formed by adding aliquid having a pigment dispersed in a water-insoluble organic solvent,to a micelle, for instance, formed of block polymer in water. It can beformed by still another method of forming an enclosed state byphase-inverting a dispersion in a state of a block polymer beingdissolved and a coloring material being dispersed in an organic solvent,into a state of being dispersed in a water-based solvent. The enclosedstate can be confirmed with various instrumental analysis methods suchas an electron microscope and X-ray diffraction. When the coloringmaterial is included in a micelle, the enclosed state can be confirmedby separating a polymer and a coloring material independently from asolvent in a micelle-decomposing condition. As discussed above, theblock polymer preferably forms a micelle state, and for that purpose,the block polymer used in the present invention is preferablyamphiphilic.

The amount of a solid coloring material enclosed in particles ispreferably 90 wt % or more, more preferably 95 wt % or more and furtherpreferably 98 wt % or more. The quantitative ratio as well can bedetermined through various electron microscopes, instrumental analysissuch as X-ray diffraction, and analysis for the coloring concentrationof a coloring material.

An ink according to the present invention is characterized in that thepigment is enclosed by block polymer. Because the pigment is enclosed byblock polymer, the coloring material can inhibit the decomposition ofitself. The smaller is the particle size, the more improved are thecoloring properties. The dispersion stability, coloring strength andcolor vividness of a coloring material-dispersed ink are greatlyaffected by the particle size of the dispersed particle and theuniformity of the particle size. Specifically, the particles with largeparticle sizes dispersed in a solvent cause coagulation between theparticles and cannot be stably dispersed. In addition, because aparticle size and coloring strength are in inverse proportion (Annalender Physik, vol. 25, p. 377, 1908), a large particle size reduces thecoloring strength. The average primary particle size of the pigment ispreferably 50 nm or smaller, further preferably 40 nm or smaller, morepreferably 30 nm or smaller, and furthermore, preferably 20 nm orsmaller. The average primary particle size of the pigment can bemeasured, for instance, with a scanning or transmission electronmicroscope. In addition, micelle particles have preferably the averageparticle size of 200 nm or smaller. An ink containing pigment enclosedby block polymer is produced by the steps of adding the pigment to asolution in the state of the block polymer being dissolved in a solvent,dispersing it therein, and insolubilizing the above described blockpolymer, or adding the pigment to a solvent dispersion containing theblock polymer forming a micelle and dispersing it therein. The enclosedstate can be confirmed with various instrumental analysis methods suchas an electron microscope and X-ray diffraction. When the coloringmaterial is included in a micelle, the enclosed state can be confirmedby separating a polymer and a coloring material independently from a.solvent in a micelle-decomposing condition. As discussed above, theblock polymer preferably forms a micelle state, and for that purpose,the block polymer used in the present invention is preferablyamphiphilic.

A preferred embodiment of an ink composition according to the presentinvention is an ink composition for an ink-jet device, and a furtherpreferable embodiment is an ink of coping with an on-demand type ink-jetdevice. Examples of the on-demand type ink-jet device include a thermaltype and a piezo type. In any type, very low viscosity is required forthe ink, which is typically 5 cps or lower. The ink composition of apreferred embodiment according to the present invention disperses asolid coloring material enclosed by amphiphilic block polymer, so thatit can realize such a dispersed state as to obtain low viscosity. Inaddition, the ink composition having a decreased variance of themolecular weight of a block polymer is preferable in respect ofviscosity.

In addition, the above described coloring material-enclosing blockpolymer particle has an average particle size of preferably 200 nm orsmaller. When the block polymer particle has the average particle sizeof 200 nm or smaller, it can improve coloring properties and inhibitscattering of visible light, and consequently can realize adequate colorexpression. The average particle size is further preferably 150 nm orsmaller, and more preferably 100 nm or smaller.

The particle size can be measured, for instance, with a dynamiclight-scattering method. When the ink composition is used for an ink-jetdevice, the block polymer particle had better have a narrower particlesize distribution, so that a dispersion index (μ/G2) which indicates theparticle size distribution is 0.2 or less, preferably 0.1 or less,further preferably 0.05 or less, and further preferably 0.01 or less.The measure for the uniformity of the particle size, or equivalently,the dispersion index μ/G2 (μ: secondary coefficient of cumulantexpansion, and G: attenuation coefficient) is based on a literaturewritten by Gulari and others (The Journal of Chemical Physics, vol. 70,p. 3,965, 1979). This value is also determined by a dynamiclight-scattering method. An apparatus for measuring a particle size withthe dynamic light-scattering method includes an apparatus such asDLS7000 made by Otsuka Electronics Co., Ltd. In addition, the particlesize can be measured through electron microscope observation.

In addition, a particle size and particle size distribution can be alsomeasured through observation by a transmission electron microscope, ascanning electron microscope and the like.

Next, the second of the present invention is a method for producing theabove described ink composition, by insolubilizing both the coloringmaterial in the state of a solution and the above described blockpolymer in the state of being dissolved, and a method for producing theabove described ink by adding the coloring material in the abovedescribed solution state into a solvent dispersion liquid having a blockpolymer forming a micelle, and dispersing it therein. The ink whichcontains a solid coloring material-enclosing block polymer, can beproduced in the above described method.

The third of the present invention is a method for forming an image byan ink-jet method with the use of the above described ink. In the nextplace, an image-forming method according to the present invention willbe described.

[Image-Forming Method]

An ink according to the present invention can be used in image-formingdevices with the use of various ink-jet methods. An image can be formedby the image-forming method with the use of the device. The ink-jetmethod to be used may be a well-known method such as a piezo ink-jettype using a piezoelectric element, or a thermal ink-jet type ofexerting thermal energy on the ink to make it foam and record; and maybe either a continuous type or an on-demand type. In addition, an inkcomposition according to the present invention can be used in arecording system of printing the ink on an intermediate transcript andtransferring it to a final medium to be recorded such as paper.

The fourth of the present invention is a device for recording an imagethrough the above described image-forming method.

[Image-Recording Device]

An ink-jet recording device using an ink composition for the ink-jetmethod according to the present invention includes an ink-jet recordingdevice of a piezo ink-jet type using a piezoelectric element, and of athermal ink-jet type of exerting thermal energy on the ink to make itfoam and record.

FIG. 1 shows a schematic functional diagram of an ink-jet recordingdevice. Reference numeral 50 denotes a central processing unit (CPU) ofan ink-jet recording device. A program for controlling CPU 50 may bememorized in a program memory 66, or as a so-called firm-ware, may bestored in a memory such as EEPROM (not shown). An ink-jet recordingdevice receives data to be recorded from a recording-data-creating means(not shown, but a computer or the like) and stores them in the programmemory 66. The recording data may be an image to be recorded, textualinformation as they are, compressed information thereof, or encodedinformation. In the case of processing the compressed or encodedinformation, the recording device can obtain the image to be recorded orthe textual information by making CPU 50 carry out extension orexpansion. If an X encoder 62 (for instance, in an X-direction or a mainscanning direction) and a Y encoder 64 (for instance, in a Y-directionor a sub-scanning direction) are installed, they can inform the relativeposition of a head with respect to a medium to be recorded, to CPU 50.

The CPU 50, on the basis of the information from the program memory 66,the X encoder 62 and the Y encoder 64, transmits signals for recordingan image to an X motor-driving circuit 52, a Y motor-driving circuit 54and a head-driving circuit 60. The X motor-driving circuit 52 and the Ymotor-driving circuit 54 respectively drive the X-direction drivingmotor 56 and the Y-direction driving motor 58 to move the head 70relatively to the medium to be recorded into the recording position. Thehead drive circuit 60 transmits signals for making the head 70 dischargevarious ink compositions (Y, M, C, K) or stimulus-giving materials whichwork as stimulus to the head 70 when it has moved to the recordingposition, and carries out recording. The head 70 may discharge amonochromatic ink composition.

Referring to examples, the present invention will be described in detailbelow, but the present invention is not limited to the examples.

EXAMPLE 1

<Synthesis of Block Polymer>

Synthesis of single-end carboxylic acid block polymer consisting of2-ethoxyethylvinylether (EOVE), 2-methoxyethylvinylether (MOVE) and HO(CH₂)₅COOH

Poly [EOVE (2-ethoxyethyl vinyl ether)-b-MOVE (methoxy ethyl vinylether)]—O (CH₂)₅COOH, (where b is a sign showing a block polymer), wassynthesized by the steps described below.

Nitrogen was substituted for air in the glass vessel having a three waystopcock attached, and the glass vessel was heated to 250° C. in anitrogen gas atmosphere to remove adsorbed water. The system was cooledback to a room temperature, then 12 mmol (millimole) of EOVE, 16 mmol ofethyl acetate, 0.1 mmol of 1-isobutoxy ethyl acetate and 11 ml oftoluene were added to the system, and the reaction system was cooled.When the temperature in the system reached 0° C., 0.2mmol of ethylaluminum sesquichloride (the equimolar mixture of diethyl aluminumchloride and ethyl aluminum dichloride) was added to start thepolymerization. The molecular weight was monitored over time with theuse of a molecular-sieve column chromatography (GPC), to confirm thecompletion of the polymerization of a component A (EOVE).

Subsequently, 12 mmol of a component B (MOVE) was added to polymerize itwith the component A. The completion of the polymerization of thecomponent B was confirmed by the monitoring with GPC, and then 30 mmolof HO (CH₂)₅COOEt was added to stop the polymerization. A reactedmixture solution was diluted with dichloromethane, and the product waswashed with 0.6 M hydrochloric acid three times and subsequently withdistilled water three times. The obtained organic phase was concentratedto dryness with an evaporator to obtain a block polymer of poly[EOVE-b-MOVE]—O (CH₂)₅COOEt.

The synthesized compound was identified by NMR and GPC. Particularly, anend portion thereof was identified by observing the end portion in aspectrum of the polymer with a DOSY method of NMR. Mn was 2.1×10⁴, andMw/Mn was 1.4. Mn is number average molecular weight, and Mw is weightaverage molecular weight.

The ester portion at the end of the obtained poly [EOVE-b-MOVE]—O(CH₂)₅COOEt was hydrolyzed, and the obtained product was identified byNMR as poly [EOVE-b-MOVE]—O (CH₂)₅COOH of interest.

The resulting block polymer with a carboxylic acid end in 26 parts byweight was stirred with 200 parts by weight of a sodium hydroxidesolution of pH 11 at 0° C. for three days, to produce a polymer solutionin the form of sodium carboxylate in which the polymer was completelydissolved. The polymer was extracted from the solution withdichloromethane and the resulting solution with the polymer extractedwas dried. Then, the solvent was evaporated to isolate the polymer.

The polymer in 25 parts by weight and 10 parts by weight of Oil Blue N(made by Sigma-Aldrich Corporation), a lipophilic dye, were dissolved in80 parts by weight of dichloromethane, the resulting solution wassubsequently added dropwise into 800 parts by weight of distilled waterwith stirring, and 200 parts by weight of ethylene glycol was furtheradded to it. The liquid in the above state was left in an open state forthree hours at 40° C. to completely remove dichloromethane and solidifya coloring material, and thus an ink composition 1 according to thepresent invention was prepared.

The ink composition 1 was cooled to 0° C., the EOVE segment of a blockpolymer was made hydrophilic, a micelle was decomposed, and the blockpolymer was dissolved in water. Then, the phase of the solid coloringmaterial was separated and the water phase was completely decolorized.From this fact, it was understood that the coloring material wascompletely included in the micelle of the block polymer. The ratio ofconcentration of the coloring material in the above described discoloredwater phase to that in the ink composition 1 was 0.8%, by the intensityratio of λmax, which proved that 99% or more of the coloring materialwere enclosed by the block polymer.

EXAMPLE 2

The ink composition prepared in the Example 1 was charged into the inktank of an ink-jet printer (BJF800, made by Canon Inc.), and was printedon plain paper. When the surface layer of a recorded part was observedwith an electron microscope, a layer coated with a block polymer wasobserved.

COMPARATIVE EXAMPLE 1

The solution, in which the lipophilic dye used in the Example 1 wasdissolved in dichloromethane, was applied on plain paper with a brush.The paper was left in an atmosphere containing 10 ppm of ozone for 30hours. The change of optical density for the coloring material on theabove described paper was measured with a portable reflection densitymeter (RD-19 made by Sakata Ink Co.), and was compared to that on therecorded medium used in the Example 2, to show three times higherdecreasing rate than that in the Example 2.

EXAMPLE 3

<Synthesis of Block Polymer>

Synthesis of single-end carboxylic acid block polymer consisting of2-ethoxy ethyl vinyl ether (EOVE), 2-methoxy ethyl vinyl ether (MOVE)and HO (CH₂) ₅COOH

Poly [EOVE (2-ethoxy ethyl vinyl ether)-b-MOVE (methoxy ethyl vinylether)]—O (CH₂)₅COOH, (where b is a sign showing a block polymer), wassynthesized via the steps described below.

Nitrogen was substituted for air in the glass vessel having a three waystopcock attached, and the glass vessel was heated to 250° C. in anitrogen gas atmosphere to remove adsorbed water. The system was cooledback to a room temperature, then 12 mmol (millimole). of EOVE, 16 mmolof ethyl acetate, 0.1 mmol of 1-isobutoxyethylacetate and 11 ml oftoluene were added to the system, and the reaction system was cooled.When the temperature in the system reached 0° C., 0.2 mmol of ethylaluminum sesquichloride (the equimolar mixture of diethyl aluminumchloride and ethyl aluminum dichloride) was added to start thepolymerization. The molecular weight was monitored in a time-divisionmanner with the use of a molecular-sieve column chromatography (GPC), toconfirm the completion of the polymerization of a component A (EOVE).

Subsequently, 12 mmol of a component B (MOVE) was added to polymerize itwith the component A. The completion of the polymerization of thecomponent B was confirmed by the monitoring with GPC, and then 30 mmolof HO (CH₂)₅COOEt was added to stop the polymerization. A reactedmixture solution was diluted with dichloromethane, and the dilutedsolution was washed with 0.6 M hydrochloric acid three times andsubsequently with distilled water three times. The obtained organicphase was concentrated to dryness with an evaporator to obtain the blockpolymer of poly [EOVE-b-MOVE]—O (CH₂)₅COOEt. The synthesized compoundwas identified by NMR and GPC. Particularly, an end portion thereof wasidentified by observing the end portion in a spectrum of the polymerwith a DOSY method of NMR. Mn was 2.1×10⁴, and Mw/Mn was 1.4. Mn isnumber average molecular weight, and Mw is weight average molecularweight.

The ester portion at the end of the obtained poly [EOVE-b-MOVE]—O(CH₂)₅COOEt was hydrolyzed, and the obtained product was identified byNMR as poly [EOVE-b-MOVE]—O (CH₂)₅COOH of interest.

The resulting block polymer with a carboxylic acid end in 26 parts byweight was mixed and stirred with 200 parts by weight of a sodiumhydroxide solution of pH 11 at 0° C. for three days, to produce apolymer solution in the form of sodium carboxylate, in which the polymerwas completely dissolved. The polymer was extracted from the solutionwith dichloromethane and the resulting solution with the polymerextracted was dried. Then, the solvent was evaporated to isolate thepolymer.

The polymer in 25 parts by weight was dissolved in 80 parts by weight ofdichloromethane, and then 10 parts by weight of phthalocyanine blue(made by Toyo Ink Mfg. Co., Ltd., and having the average primaryparticle size of 48 nm when measured with an electron microscope) wasadded to the solution and dispersed therein. The mixture was addeddropwise into 800 parts by weight of distilled water with stirring, and200 parts by weight of ethylene glycol was further added to it. Theliquid was left in an open state for three hours at 40° C. to completelyremove dichloromethane, and thus an ink composition 2 according to thepresent invention was prepared. When the particle size of the dispersionink was measured with dynamic light scattering, an average micelle sizewas 140 nm, and the dispersion index was 0.20. The ink wascryotransferred into and observed with an EF-TEM, and as a result,spherical micelles (with the average size of 130 nm) were observed.Elemental analysis of the sample EELS revealed that the pigment wasincluded in the block polymer micelle. The ink was cooled to 0° C., theEOVE segment of a block polymer was made hydrophilic, the micelle wasdecomposed, and the block polymer was dissolved in water. Then, thephase of the pigment was separated and the water phase was completelydecolorized. From this fact, it was understood that the coloringmaterial was completely included in the micelle of the block polymer.The ratio of concentration of the coloring material in the abovedescribed discolored water phase to that in the dispersion ink was 0.8%,by the intensity ratio of λmax, which proved that 99% or more of thecoloring material were enclosed by the block polymer.

EXAMPLE 4

The ink prepared in the Example 3 was charged into the ink tank ofBJF800 made by Canon Inc., and was printed on plain paper. When thesurface layer of a recorded part was observed with an electronmicroscope, a layer coated with a block polymer was observed.

EXAMPLE 5

By using the polymer used in the Example 3 and a pigment LIONOGEN YELLOW1010 (which has the primary particle size of 21 nm when measuredelectron-microscopically) made by Toyo Ink Mfg. Co., Ltd., an inkincluding a coloring material was prepared similarly to the Example 3.When the particle size of the dispersion ink was measured with dynamiclight scattering, an average micelle size was 98 nm, and the dispersionindex was 0.09. Similarly to the Example 4, the ink was charged into theink tank of BJF800 made by Canon Inc., and was clearly printed on plainpaper.

COMPARATIVE EXAMPLE 2

The solution, in which the pigment used in the Example 3 was dispersedin dichloromethane, was cryotransferred into and observed with an EF-TEMsimilarly to the Example 4, and as a result, needle crystals wereobserved, but spherical micelles observed in the Example 1 were notobserved. As a result, it was assumed that the pigment was not coatedbut was in a crystal state.

The ink was applied on plain paper with a brush. The paper was left inan atmosphere containing 10 ppm of ozone for 30 hours. The change ofoptical density for the coloring material on the above described paperwas measured with RD-19 made by Sakata Ink Co., and was compared to thaton the recorded medium used in the Example 2, to show two times higherdecreasing rate than that in the Example 2.

The results of the examples and the comparative examples described abovecan differ in some degree according to the difference of thespecification and the maker of measuring instruments.

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide an ink compositionwhich contains a solid coloring material, a block polymer and a solvent,and has the adequate dispersibility of the coloring material.

In addition, the present invention can provide an ink composition for anink-jet device, which has adequate fixability and further adequate tintand coloring of a printed image.

In addition, the present invention can easily provide a method forproducing an ink composition superior in the dispersibility of the abovedescribed coloring material.

In addition, the present invention can provide an image-forming methodwith the use of the above described ink composition, and animage-forming device used for it.

1. A composition characterized in that the particles of a solid coloringmaterial are enclosed in a micelle formed of a block polymer.
 2. Thecomposition according to claim 1, wherein 90 wt % or more of the solidcoloring material are enclosed by the block polymer.
 3. The compositionaccording to claim 1, wherein the average particle size of the particlesis 200 nm or less.
 4. The composition according to claim 3, wherein theparticle size distribution has a dispersion index μ/G2 of 0.2 or less.5. The composition according to claim 1, wherein the block polymercontains a repeating unit structure of a polyvinyl ether.
 6. A methodfor producing a composition having the particles of a solid coloringmaterial enclosed in a micelle formed of a block polymer, characterizedby a step of forming particles by insolubilizing the coloring materialand the block polymer in a state of both being dissolved or uniformlydispersed.
 7. A method for producing a composition having the particlesof a solid coloring material enclosed in a micelle formed of a blockpolymer, characterized by a step of forming particles by adding anddispersing a coloring material dissolved in a solution into a solventdispersion having the block polymer forming a micelle.
 8. Animage-forming method for recording the image by giving an ink onto amedium to be recorded, characterized in that the ink is a compositioncontaining the particles of a solid coloring material enclosed in amicelle formed of a block polymer.
 9. An image-forming device forrecording the image by giving an ink onto a medium to be recorded,characterized in that the ink is a composition containing the particlesof a solid coloring material enclosed in a micelle formed of a blockpolymer.
 10. The composition according to claim 1, characterized in thatthe particle of the solid coloring material is pigment.
 11. Thecomposition according to claim 10, characterized in that the averageprimary particle size of the pigment is 50 nm or smaller.